High efficiency permanent magnet machine

ABSTRACT

The present invention is a high efficiency permanent magnet machine capable of maintaining high power density. The machine is operable over a wide range of power output. The improved efficiency is due in part to copper wires with a current density lower than traditional designs and larger permanent magnets coupled with a large air gap. In a certain embodiment wide stator teeth are used to provide additional improved efficiency through significantly reducing magnetic saturation resulting in lower current. The machine also has a much smaller torque angle than that in traditional design at rated load and thus has a higher overload handling capability and improved efficiency. In addition, when the machine is used as a motor, an adaptive phase lag compensation scheme helps the sensorless field oriented control (FOC) scheme to perform more accurately.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application is a continuation of and claims priorityto nonprovisional application No. 14/146,059 entitled “HIGH EFFICIENCYPERMANENT MAGNET MACHINE,” filed Jan. 2, 2014, which in turn claimpriority to provisional application No. 61/748,998, entitled “HIGHEFFICIENCY LOW SPEED PERMANENT MAGNET MACHINE,” filed Jan. 4, 2013, andto provisional application No. 61/803,993 entitled “HIGH EFFICIENCYPERMANENT MAGNET MACHINE,” filed Mar. 21, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, generally, to electrical machines. Morespecifically, it relates to a high efficiency electrical motor orgenerator.

2. Brief Description of the Prior Art

Electrical motors and generators are machines capable of convertingelectrical energy into mechanical energy and converting mechanicalenergy into electrical energy, respectively. These electrical machineshave many similarities and can often be operated as either an electricalgenerator or motor.

Known electrical machines include a rotor, a stator, a plurality ofelectrical windings, and a plurality of permanent magnets. The rotor isa generally cylindrical shape with an outer circumference and an axialbore creating an inner circumference. The inner circumference is adaptedto receive a shaft such that the two may rotate as one. The outercircumference of the rotor contains a plurality of permanent magnets(PMs) disposed longitudinally parallel to the axis of rotation orcentral axis of the rotor in a preferably generally uniform andconcentric manner.

Current stator designs have a generally cylindrical shape with an outercircumference and a predetermined number of teeth projecting, apredetermined distance, inwardly towards the longitudinal axis of thestator. The teeth create a discontinuous inner circumference allowingthe rotor and PM assembly to be disposed within the stator such that therotor assembly is freely rotatable within the inner circumference ofstator. Between each tooth is a stator slot having predetermined shapeand size adapted to receive electrical windings. Electrical windings aretypically strands of conductive materials, such as copper or aluminum,which are arranged into coil groups around the stator teeth. Theelectrical windings interact with the PMs to produce either mechanicalor electrical energy. When configured as a motor, the electrical machineuses current flowing through the electrical windings to generaterotating magnetic fields which interact with the PMs attached to therotor and cause the rotor and shaft to rotate. When configured as agenerator, the PMs, and their respective magnetic fields, are rotatedand interact with the electrical windings to produce electricity.

In recent years, the push towards green energy has increased the demandassociated with developing efficient electric machine technology. TheU.S. Department of Energy estimates that electric motors in the U.S.consume more than half of all electrical energy in the states.Therefore, improving the efficiency of these electric machines willgreatly decrease the United States' carbon footprint.

Currently, some commercial off-the-shelf electric motors are designedfor high efficiency, but have power densities on the order of only 0.1horse power per pound (HP/lb.). Electric motors developed for use inaircraft propulsion (small unmanned aerial vehicles), on the other hand,have power densities between 1 and 2 HP/lb., while direct-drive electricmotors can attain power densities greater than 5 HP/lb. only throughincreased operating speeds.

Traditionally in electric machine applications, the higher the electricmachine's efficiency, the less energy wasted and the easier the thermalmanagement system; however, the efficiency generally comes at the costof increased size and weight. Copper loss is the term often given toheat produced by electrical currents in the conductors of transformerwindings, or other electrical devices. Copper losses are an undesirabletransfer of energy, as are core losses, which result from inducedcurrents in adjacent components. Copper loss is the most significant inall the losses in electric machines, so reducing the copper loss is thekey to building highly efficient machines. It is known that copper lossis inversely proportional to the wire's cross-sectional area. Therefore,copper wires having a greater cross-sectional area (large diameter) andlower current density will also require a larger slot area. The largerslot area requires the stator size to increase or tooth size todecrease. If the stator size increases, the machine becomes larger andthe power density decreases. If the tooth size decreases, the magneticsaturation increases, and so the current must increase resulting indecreased efficiency.

Accordingly, what is needed is a highly efficient scalable permanentmagnet machine having relatively high power density while being capableof operating at a wide range of power outputs. However, in view of theart considered as a whole at the time the present invention was made, itwas not obvious to those of ordinary skill in the field of thisinvention how the shortcomings of the prior art could be overcome.

All referenced publications are incorporated herein by reference intheir entirety. Furthermore, where a definition or use of a term in areference, which is incorporated by reference herein, is inconsistent orcontrary to the definition of that term provided herein, the definitionof that term provided herein applies and the definition of that term inthe reference does not apply.

While certain aspects of conventional technologies have been discussedto facilitate disclosure of the invention, Applicants in no way disclaimthese technical aspects, and it is contemplated that the claimedinvention may encompass one or more of the conventional technicalaspects discussed herein.

The present invention may address one or more of the problems anddeficiencies of the prior art discussed above. However, it iscontemplated that the invention may prove useful in addressing otherproblems and deficiencies in a number of technical areas. Therefore, theclaimed invention should not necessarily be construed as limited toaddressing any of the particular problems or deficiencies discussedherein.

In this specification, where a document, act or item of knowledge isreferred to or discussed, this reference or discussion is not anadmission that the document, act or item of knowledge or any combinationthereof was at the priority date, publicly available, known to thepublic, part of common general knowledge, or otherwise constitutes priorart under the applicable statutory provisions; or is known to berelevant to an attempt to solve any problem with which thisspecification is concerned.

BRIEF SUMMARY OF THE INVENTION

The long-standing but heretofore unfulfilled need for a more efficientpermanent magnet electric machine is now met by a new, useful, andnonobvious invention.

The novel structure includes a laminated cylindrical rotor and alaminated cylindrical stator enclosed in a housing. The rotor has anaxial bore adapted to receive a shaft and an outer circumference adaptedto receive a plurality of permanent magnets. Each permanent magnet has amagnetic flux density between 70 and 95 percent of a residual magneticflux density of the rotor's permanent magnet material.

The stator includes an outer circumference, a slot pitch, a longitudinalaxis, and plurality of teeth projecting a predetermined distanceinwardly towards the longitudinal axis of the stator. The teeth create adiscontinuous inner circumference allowing the rotor to be disposedwithin the stator such that a central axis of the rotor aligns with thestator's longitudinal axis. The rotor is freely rotatable within theinner circumference of stator. The stator also includes stator slots ofpredetermined shape and size disposed between each tooth and adapted toreceive a predetermined number of strands of conducting material to forman electrical winding around each tooth.

An air gap exists between the outer circumference of the rotor and theinner circumference of the stator when the rotor is disposed within thestator, such that the air gap is inversely proportional to the torqueangle of the machine. The torque angle is between about 2 and about 10degrees, which is significantly less than the standard, and isproportional to the thickness of the permanent magnets.

Additionally, the electrical machine includes a predetermined number ofpoles, where the number of poles is directly proportional to theelectrical frequency of the electric machine and inversely proportionalto a number of required coil windings. The present invention utilizes athree phase electrical winding scheme where each phase has two groupsand each group includes two coils connected in series. The windings arecomprised of strands of conducting material having a cross-sectionalarea that is related to current density with the preferred currentdensity ranging between about 3 and about 8 Amp/mm².

In a certain embodiment the stator teeth each have a generally uniformwidth, wherein the magnitude of the width is between about 60 and about80 percent of the magnitude of the slot pitch. This design featureprovides decreased magnetic saturation and therefore increasedefficiency.

In a certain embodiment the present invention may utilize a sensorlessfield oriented control, where a rotor angle is estimated by a slidingmode observer and the sliding mode observer module contains a firstorder low-pass filter for back electromotive force estimation. In suchan embodiment a phase lag compensation value, that is automaticallycalculated based on rotational speed of the rotor, is applied tofeedback resulting in increased accuracy of the field oriented control.

These and other important objects, advantages, and features of theinvention will become clear as this disclosure proceeds.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts that will beexemplified in the disclosure set forth hereinafter and the scope of theinvention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference should be made tothe following detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 depicts an exemplary B-H curve.

FIG. 2 a depicts a phasor diagram illustrating torque angle betweeninduced voltage E_(A) and terminal voltage V_(φ) and between net fluxλ_(net) and rotor flux λ_(f) .

FIG. 2 b depicts a phasor diagram illustrating the relationship betweentorque angle and magnetic flux density.

FIG. 3 is a perspective view of a first embodiment of the presentinvention.

FIG. 4 is an exploded view of the first embodiment in FIG. 3.

FIG. 5 is a perspective view of a second embodiment of the presentinvention.

FIG. 6 is an exploded view of the second embodiment in FIG. 3.

FIG. 7 is a top view the first embodiment illustrating the rotordisplaced inside the stator.

FIG. 8 is a close up view of the second embodiment illustrating the airgap between the stator teeth and the permanent magnets on the rotor.

FIG. 9 is a close up view of the first embodiment illustrating the airgap between the stator teeth and the permanent magnets on the rotor.

FIG. 10 is a top view the second embodiment illustrating the rotordisplaced inside the stator.

FIG. 11 depicts a winding scheme diagram of the second embodiment withthe stator slots being identified by numerical indicators 1-36.

FIG. 12 emphasizes Phase A of the winding scheme diagram shown in FIG.11.

FIG. 13 emphasizes Phase B of the winding scheme diagram shown in FIG.11.

FIG. 14 emphasizes Phase C of the winding scheme diagram shown in FIG.11.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings, which form a partthereof, and within which are shown by way of illustration specificembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The present invention is a high efficiency electrical machine operableas a motor or generator. The electrical machine includes a rotor, astator, a plurality of electrical windings, and a plurality of permanentmagnets all contained in a housing. The rotor has a generallycylindrical shape with an outer circumference and an axial bore creatingan inner circumference. The inner circumference is adapted to receive ashaft such that the two may rotate as one. The outer circumference ofthe rotor contains a plurality of permanent magnets (PMs) disposedlongitudinally parallel to the axis of rotation or central axis of therotor in a preferably generally uniform and concentric manner. In acertain embodiment the PM's are arranged in a manner such that theoutward radially facing magnetic poles are alternating in orientationbetween each PM.

The stator has a generally cylindrical shape with an outer circumferenceand a predetermined number of teeth projecting, a predetermineddistance, inwardly towards the longitudinal axis of the stator. Theteeth create a discontinuous inner circumference allowing the rotor andPM assembly to be disposed within the inner circumference of the statorsuch that the rotor assembly is freely rotatable within the innercircumference of stator. Between each tooth is a stator slot ofpredetermined shape and size adapted to receive a predetermined numberof, preferably copper, conducting strands or wires to form a windingaround a predetermined number of teeth.

The present invention utilizes a design providing decreased copper lossand decreased windage loss to improve the overall efficiency of theelectrical machine. In order to decrease copper loss, the presentinvention uses copper wires having a larger diameter than traditionaldesigns. The wires have a diameter related to current density as shownin the equation below:

$\begin{matrix}{J = \frac{4\; I}{\pi \; d^{2}}} & (1)\end{matrix}$

As shown in equation 1, low current density will result in large wirediameter which will reduce the copper loss since the copper loss isinversely proportional to the wire's cross-sectional area. The preferredvalue of current density is in the range of 3 to 8 Amp/mm². Inelectrical machine design, winding current density is an importantfactor. Due to the heat dissipation limitation, current density must notexceed a certain value, otherwise the motor will overheat. For aircooling, the current density is usually lower than 8 A/mm² and thecurrent density has such a relationship with the wire diameter as seenin equation (1). So, under the same current, larger wire diameter couldresult in a lower current density which provides the motor with moreoverload capability (capable of operating with a higher current), andless heat stress. Additionally, to reduce the eddy current effects andproximity effects resulting in increased efficiency, a certainembodiment may utilize a known stranded Litz wire instead of solid wire.

Although a thicker wire requires a larger stator slot area, a highlyefficient machine generates much less heat and therefore does not needto use any active cooling methodologies (such as fan, liquid cooling orspray cooling); and hence the overall power density of the whole system(including cooling devices) may not decrease much. A passive coolingmechanism, such as fins on the machine's outside housing, is sufficientwhen the efficiency is high. In a certain embodiment, the housing maycontain a passive cooling mechanism or an active cooling mechanism,depending on the application of the electrical machine.

In order to counteract the need to increase the slot area to account forlarger wires, the number of turns in each coil, or in other words theamount of wire in the slot area, is decreased. However, decreasing thenumber of turns per coil requires higher electrical frequency. Theelectrical frequency depends on the number of rotor pole pairs (PP) andmechanical frequency (MF) of the rotor as shown in the equation below:

EF=PP×MF   (2)

The electrical frequency is not exactly a constant when the motor runs.Instead a motor is typically driven using a motor drive system, whichprovides electrical frequency specified by a controller. For example, inan application for truck APU, the motor speed is almost a constant. Ifusing a large number of pole pairs, the electric frequency willincrease. The number of turns per coil for the stator winding isinversely proportional to the electric frequency as shown below inequation 3.

$\begin{matrix}{N_{c} = \frac{1.1\; V_{\varphi \; {rated}}}{2\sqrt{2}\pi \; f_{e}{nk}_{w}B_{m}{Dl}}} & (3)\end{matrix}$

Where N_(c) is the effective turns per coil, V_(φrated) is phasevoltage, f_(e) is electrical frequency, n is number of group windingsper pole, k_(w) is the back EMF due to stator pitch, B_(m) is a sum ofresidual magnetic flux density, D is the diameter of the motor, and l isthe length of the motor.

Thus, with higher electric frequency, a lower number of coil turnssuffices, therefore leading to smaller slot areas. Ultimately, anincrease in the number of pole pairs, resulting in increased electricalfrequency, allows the present invention to utilize a decreased number ofturns per coil, thus resulting in a smaller required slot area andpreventing the need to increase the overall size of the machine.

The preferred embodiment of the present invention uses 8 to 16 rotorpoles when the intended mechanical speed is less than 3,000 revolutionsper minute. Although the present invention may seem to use acomparatively large slot area for a low speed machine, when theelectrical frequency is increased, the number of turns decreases, andthe slot area required can be comparable to that of a 2 to 6 pole designutilizing a smaller diameter copper wire.

Moreover, the design utilizes a smaller torque angle, a large air gapand large PM's to increase efficiency. Traditionally, the high cost ofPM's has led innovators to develop electric machines with small PM'sultimately forcing the design to contain a small air gap (0.5 mm-10 mm).However, a small air gap leads to a higher windage loss (shear forces onthe air between the rotor and stator), which results in less efficientelectric machines. To avoid demagnetization the present inventionutilizes a B_(mR) (the magnetic flux density from the rotor PM's)between about 70 and 95 percent of Br (the residual magnetic fluxdensity of the permanent magnet material on the rotor). Then, using thematerial's B-H curve as shown in FIG. 1, H_(mR) (the magnetic fieldintensity in the PM's) is determined. The following equation representsthe relationship between the size of the air gap and the size of thePM's when the total magnetomotive force (MMF) in the loop is zero.

g _(eff) B _(mR)+μ₀ H _(mR) l _(m)=0   (4)

Where g_(eff) is effective air gap, which is proportional to the realair gap, and l_(m) is the PM thickness. Because B_(mR) and H_(mR) have acertain relationship and can be considered constant for a particulardesign, and H_(mR) is negative (See FIG. 1), it is apparent that the airgap and PM thickness are proportional.

Torque angle is also related to air gap and therefore permanent magnetsize. Traditional electric machines utilize a torque angle between about15 and 30 degrees at the machine's rated power and speed. The presentinvention uses a much lower torque angle of 2 to 10 degrees at ratedpower and speed. Torque angle is δ as shown in FIG. 2 a, and can berepresented as the angle between the induced voltage E_(A) and terminalvoltage V_(φ) or the angle between net flux λ_(net) direction (totalflux, which is the result of interaction between flux from windingexcitation and rotor flux) and the rotor flux λ_(f) direction. Thetorque angle can also be seen as the angle that the rotor poles lagsbehind the rotating field.

When torque angle is 0 degrees, there is no torque, but at 90 degrees,the torque is at its maximum. However if the torque angle goes over 90degrees, the motor will lose synchronization and stop. When the motor isrunning at a small torque angle at rated load, it has more room andpotential to provide more torque if needed (when the load torqueincreases, the motor will have a larger torque angle for compensationand try to produce more torque output). However, torque angle needs tobe kept at a certain range because if it increases too much there isdanger of losing synchronization. Therefore, having the motor running ata small torque angle for rated power, means it has better overload powerhandling capability and efficiency.

As shown in FIG. 2 b, the magnetic flux density from the rotor (B_(R))and the magnetic flux density in the stator armature (B_(S)) have thefollowing relationship:

B _(S) =B _(R) sin δ  (5)

Where B_(mR) (which is B_(R) in this equation) is determined when theworking point is chosen and can be considered as a constant in aparticular design. Therefore, a small torque angle δ will result in asmaller B_(S). Additionally, the magnetic flux density generated fromthe armature windings has a relationship with air gap as shown below.

$\begin{matrix}{{\hat{g}}_{total} = {\frac{4}{\pi}\frac{\mu_{0}}{B_{a,{pk}}}\frac{{\hat{N}}_{a}}{P}1.5\sqrt{2\;}I_{A,{rated}}}} & (6)\end{matrix}$

Where ĝ_(total is) the effective total airgap, {circumflex over (N)}_(a)is effective number of series turns per phase of armature winding, P isthe number of rotor poles, I_(A,rated) is the rated phase current, μ₀ isa vacuum permeability constant, and B_(a,pk) is the B_(S) describedabove. Equation (6) proves that a smaller B_(a,pk) will result in alarger air gap. Therefore, smaller torque angle will lead to a smallerB_(S), which results in a larger air gap.

The present invention's use of a small torque angle between about 2degrees and about 10 degrees, a large air gap based on the torque anglefrom equations (5-6), and large PM's based on the air gap from equation(4). The large air gap, as accentuated in FIGS. 7-10, helps to reducethe windage loss and noise level, while increased PM thickness helps toavoid demagnetization.

In a certain embodiment, the present invention utilizes a sensorlessfield oriented control (FOC), where the rotor angle is estimated by asliding mode observer (SMO). The SMO module contains a first orderlow-pass filter for back EMF estimation. However, this low pass filterwill cause a delay in the estimated angle. Rotor angle is a criticalparameter in FOC control: to accurately achieve FOC control,compensation is made to the estimated angle. The phase lag differs atdifferent speeds, and therefore, the compensation must be adaptive. Theangle delay may be calibrated at different speeds utilizing a functionto interpolate the delay angle vs. speed curve. The appropriate phaselag compensation value is automatically calculated based on the speed ofthe motor and applied to the feedback. This adaptive phase lagcompensation increases the accuracy of the control.

In an embodiment of the invention intended for use in electricalmachines operating at mechanical speeds of greater than 3,000 rpm, alower number of rotor poles than specified above may be preferable. Foran electrical machine that operates at speeds greater than 6,000 rpm,2-12 poles are sufficient. Alternative embodiments may involve morepoles for electrical machines intended to operate at lower speeds. Whenthe mechanical speed is high, less poles are preferred because of themechanical strength of the rotor.

A certain embodiment may employ a laminated stator and/or a laminatedrotor, such that both are made of laminated sheets held together by anadhesive having thermal insulation properties. Such a design reduces theneed to have additional internal cooling devices to prevent the electricmachine from overheating. The laminated design also provides theadditional known benefit of reducing eddy currents.

EXAMPLE 1

As shown in FIG. 3, a certain embodiment, generally denoted as referencenumeral 100, of the present invention is a high efficiency electricalmotor having shaft 114, laminated stator 102, and laminated rotor 106all contained within housing 112. Laminated stator 102 contains aplurality of windings 104, and laminated rotor 106 contains a pluralityof permanent magnets 108. Rotor 106 is disposed within the innercircumference of stator 102 such that the longitudinal axis of stator102 is aligned with the central axis of rotor 106 and rotor 106 isfreely rotatable within stator 102. Stator 102 has a plurality of statorteeth 110 and a plurality of stator slots wherein each stator slot isdisposed between two stator teeth 110. Windings 104 are positionedaround each tooth 110 passing through stator slots on either side ofeach respective tooth 110. Windings 104 are illustrated in the figuresas having a rectangular shape for clarity purposes. The windings, beingcomposed of multiple strands of conducting material would be difficultto illustrate in the figures as they actually exist with proper clarity.

As shown in FIGS. 3, 4, 7, and 9, stator 102 has been designed tofurther reduce copper loss by using wider teeth 110. Since the copperloss is proportional to the current squared, reducing the current is aneffective way to reduce copper loss and improve efficiency. The currentis reduced by decreasing magnetic saturation and magnetic saturation isinversely related to tooth width. So the width of the stator teeth wasincreased to decrease magnetic saturation, in turn decreasing current,and ultimately decreasing copper loss. Teeth 110 have a width preferablyin the range of 60% to 80% of the stator's slot pitch. Slot pitch is acircumferential distance along the inner circumference of the statorfrom the center line of one tooth or slot to the center line of theadjacent tooth or slot. Traditional electric machine designs utilizestator teeth having widths of about 40% to 60% of the slot pitchresulting in greater magnetic saturation and less efficiency than thepresent invention.

A certain embodiment of the motor may implement a winding scheme having3 phases (A, B, C) with each phase having two groups and each groupincluding two coils connected in series. For example, a stator having 12stator slots, 3 phases, and two groups per phase would have coilsarranged as shown in Table 1 below.

TABLE 1 Winding table illustrating a concentric winding scheme for a 12slot stator. Slot Number Phase A Phase B Phase C 1 In Out 2 Out & Out 3In Out 4 In & In 5 Out In 6 Out & Out 7 Out In 8 In & In 9 Out In 10 Out& Out 11 In Out 12 In & In

In an alternate embodiment, the groups may be connected in parallel asis known by a person having ordinary skill in the art.

EXAMPLE 2

As shown in FIG. 5, a certain embodiment, generally denoted as referencenumeral 200, is a high efficiency electrical generator. Similar to themotor, the generator design includes shaft 214, stator 202, rotor 206,electrical windings 204, and PMs 208 all contained in housing 212. Therotor has four PMs 208 for use at a desired operational speed of 6,000rpm to prevent excessive electrical frequency associated with too manyrotor poles. Stator 202 is comprised of thirty six stator teeth 210 andtherefore thirty six stator slots. Similar to windings 104, windings 204are illustrated in the figures as having a rectangular shape for claritypurposes. As shown in FIG. 5, a winding encompasses two stator teeth.This illustration is simply for clarity. Embodiment 200 actuallycontains 2 coils per slot. FIGS. 11-14 illustrate the three phasewinding diagram, in which there is 1 turn per coil, 2 coils per slot,and all the groups are connected in series. Each coil contains about 120strands of conducting material. In an alternate embodiment, the groupsmay be connected in parallel as is known by a person having ordinaryskill in the art.

GLOSSARY OF CLAIM TERMS

Back Electromotive Force Estimation: is the estimation of the voltageinduced in electric motors where there is relative motion between thearmature of the motor and the magnetic field.

Current Density: is the electrical current per unit area of crosssection

Electrical Frequency: is the number of cycles of electricity per unit oftime.

Electrical Winding: is a number of strands of conducting material woundaround stator teeth.

Low-Pass Filter: is a filter that passes low-frequency signals andattenuates signals with frequencies higher than the cutoff frequency.

Magnetic Flux Density: is the amount of magnetic flux per unit areataken perpendicular to the direction of the magnetic flux.

Passive Cooling Mechanism: is heat dissipation without the aid of a pumpor fan.

Permanent Magnet: is a magnet that retains its magnetic properties inthe absence of an inducing field or current.

Phase Lag Compensation Value: is the angle that calculated based onrotor speed and feedback loop delay. It is applied to the estimatedrotor angle to increase accuracy.

Pole: point where electric or magnetic force appears to be concentrated.

Rotor: is a rotary part of a machine.

Rotor Sheet: is a thin layer of material adapted to be laminated toadditional rotor sheets to form the final rotor dimensions.

Sensorless Field Oriented Control: is a sensorless variable frequencydrive control method.

Sliding Mode Observer: is a non-linear high-gain observer.

Slot Pitch: is a distance between corresponding points in adjacentstator slots. It can also be expressed as an angle.

Stator Sheet: is a thin layer of material adapted to be laminated toadditional stator sheets to form the final stator dimensions.

Stator Slot: is an opening between two stator teeth.

Stator Tooth Width: is a measurement of the minimum width of the tooth.

Stator: is a mechanical device consisting of the stationary part of amotor or generator in or around which the rotor revolves.

Thermal Insulating Adhesive: is a substance having a tendency to stickand the capability to reduce heat transfer between objects in thermalcontact or in range of radiative influence.

Torque Angle: is the angle between the induced voltage E_(A) andterminal voltage V_(φ) or the angle between net flux λ_(net) direction(total flux, which is the result of interaction between flux fromwinding excitation and rotor flux) and the rotor flux λ_(f) direction.The torque angle can also be seen as the angle that the rotor poles lagsbehind the rotating field.

The advantages set forth above, and those made apparent from theforegoing description, are efficiently attained. Since certain changesmay be made in the above construction without departing from the scopeof the invention, it is intended that all matters contained in theforegoing description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention that, as amatter of language, might be said to fall therebetween.

What is claimed is:
 1. An electric machine, comprising: a rotor, therotor further including: having a cylindrical shape and a central axis;an axial bore adapted to receive a shaft; an outer circumference adaptedto receive a plurality of permanent magnets comprising of permanentmagnet material, wherein each permanent magnet has a magnetic fluxdensity between 70 and 95 percent of a residual magnetic flux density ofthe permanent magnet material; a stator, the stator further including:having a cylindrical shape and a longitudinal axis; an outercircumference; a plurality of teeth disposed in an equidistant angularrelationship, each tooth projecting inwardly toward the longitudinalaxis, the teeth creating a discontinuous inner circumference configuredto accept the rotor within the stator such that the longitudinal axis ofstator is aligned with the central axis of the rotor and the rotor isrotatable within the inner circumference of the stator; a stator slot ofpredetermined shape and size disposed between each tooth and adapted toreceive a predetermined number of strands of conducting material to forman electrical winding around at least one tooth; a predetermined numberof poles, whereby the number of poles is directly proportional to anelectrical frequency of the electric machine and inversely proportionalto a number of required coil windings; and an air gap between the outercircumference of the rotor and the inner circumference of the statorwhen the rotor is disposed within the stator.
 2. The electric machineaccording to claim 1, further comprising a current density rangingbetween 3 and 8 Amp/mm2.
 3. The electric machine according to claim 1,further comprising a torque angle between 2 and 10 degrees.
 4. Theelectric machine according to claim 1, further comprising a three phaseelectrical winding scheme where each phase has two groups and each groupincludes two coils connected in series.
 5. The electric machineaccording to claim 1, further comprising the rotor having a plurality ofrotor sheets affixed to one another by a thermal insulating adhesivedisposed between adjacent rotor sheets.
 6. The electric machineaccording to claim 1, further comprising the stator having a pluralityof stator sheets affixed to one by a thermal insulating adhesive layerdisposed between the adjacent stator sheets.
 7. The electric machineaccording to claim 1, further comprising a sensorless field orientedcontrol, where a rotor angle is estimated by a sliding mode observer,the sliding mode observer module containing a first order low-passfilter for back electromotive force estimation.
 8. The electric machineaccording to claim 1, further comprising a control module configured toautomatically calculate a phase lag compensation value based onrotational speed of the rotor and is applied to feedback increasingaccuracy of the field oriented control.
 9. The electric machineaccording to claim 1, further comprising a housing enclosing the statorand rotor, wherein the housing includes a passive cooling mechanism. 10.The electric machine according to claim 1, further comprising the statorteeth each having a generally uniform width, wherein the magnitude ofthe width is between 60 and 80 percent of the magnitude of a slot pitch.11. The electric machine according to claim 1, further comprising therotor having between 8 and 16 poles when the intended rotational speedof the rotor is less than 3000 rpm.
 12. The electric machine accordingto claim 1, further comprising the rotor having between 2 and 12 poleswhen the intended rotational speed of the rotor is greater than 6000rpm.
 13. An electric machine, comprising: a rotor, the rotor furtherincluding: having a cylindrical shape and a central axis; an axial boreadapted to receive a shaft; an outer circumference adapted to receive aplurality of permanent magnets comprising of permanent magnet material;a stator, the stator further including: having a cylindrical shape and alongitudinal axis; an outer circumference; a plurality of teeth disposedin an equidistant angular relationship, each tooth projecting inwardlytoward the longitudinal axis, the teeth creating a discontinuous innercircumference configured to accept the rotor within the stator such thatthe longitudinal axis of stator is aligned with the central axis of therotor and the rotor is rotatable within the inner circumference of thestator; a stator slot of predetermined shape and size disposed betweeneach tooth and adapted to receive a predetermined number of strands ofconducting material to form an electrical winding around at least onetooth; a current density ranging between 3 and 8 Amp/mm2; apredetermined number of poles, whereby the number of poles is directlyproportional to an electrical frequency of the electric machine andinversely proportional to a number of required coil windings; and an airgap between the outer circumference of the rotor and the innercircumference of the stator when the rotor is disposed within thestator.
 14. The electric machine according to claim 13, wherein eachpermanent magnet has a magnetic flux density between 70 and 95 percentof a residual magnetic flux density of the permanent magnet material.15. The electric machine according to claim 13, further comprising atorque angle between 2 and 10 degrees.
 16. The electric machineaccording to claim 13, further comprising a three phase electricalwinding scheme where each phase has two groups and each group includestwo coils connected in series.
 17. The electric machine according toclaim 13, further comprising a sensorless field oriented control, wherea rotor angle is estimated by a sliding mode observer, the sliding modeobserver module containing a first order low-pass filter for backelectromotive force estimation.
 18. The electric machine according toclaim 13, further comprising a control module configured toautomatically calculate a phase lag compensation value based onrotational speed of the rotor and is applied to feedback increasingaccuracy of the field oriented control.
 19. The electric machineaccording to claim 13, further comprising the stator teeth each having agenerally uniform width, wherein the magnitude of the width is between60 and 80 percent of the magnitude of a slot pitch.
 20. An electricmachine, comprising: a rotor, the rotor further including: having acylindrical shape and a central axis; an axial bore adapted to receive ashaft; an outer circumference adapted to receive a plurality ofpermanent magnets comprising of permanent magnet material; a stator, thestator further including: having a cylindrical shape and a longitudinalaxis; an outer circumference; a plurality of teeth disposed in anequidistant angular relationship, each tooth projecting inwardly towardthe longitudinal axis, the teeth creating a discontinuous innercircumference configured to accept the rotor within the stator such thatthe longitudinal axis of stator is aligned with the central axis of therotor and the rotor is rotatable within the inner circumference of thestator; a stator slot of predetermined shape and size disposed betweeneach tooth and adapted to receive a predetermined number of strands ofconducting material to form an electrical winding around at least onetooth; a torque angle between 2 and 10 degrees; a predetermined numberof poles, whereby the number of poles is directly proportional to anelectrical frequency of the electric machine and inversely proportionalto a number of required coil windings; and an air gap between the outercircumference of the rotor and the inner circumference of the statorwhen the rotor is disposed within the stator.